Hyperthyroidism and Risk for Bipolar Disorders: A Nationwide Population-Based Study

Background: Thyroid disorders have long been associated with psychiatric illness, often with symptoms suggestive of mood disorders. The most common clinical features associated with hyperthyroidism are anxiety and depression. The risk of bipolar disorders, especially bipolar mania, among patients with thyroid disorders has not been well characterized. Objective: We explored the relationship of hyperthyroidism and the subsequent development of bipolar disorders, and examined the risk factors for bipolar disorders in patients with hyperthyroidism. Methods: We identified patients who were diagnosed with hyperthyroidism between 2000 and 2010 in the Taiwan National Health Insurance Research Database. A comparison cohort without hyperthyroidism was matched based on age, sex, and comorbidities. The occurrence of bipolar disorders was evaluated in both cohorts based on diagnosis and the use of mood stabilizer drugs. Results: The hyperthyroidism cohort consisted of 21, 574 patients, and the comparison cohort consisted of 21, 574 matched control patients without hyperthyroidism. The incidence of bipolar disorders (incidence rate ratio [IRR], 2.31, 95% CI 1.80-2.99, P = .001) was higher for the hyperthyroidism patients than the control patients. Multivariate, matched regression models showed that women (HR 2.02, 95% CI 1.34-3.05, P = .001), patients with alcohol use disorders (HR 3.03, 95% CI 1.58-5.79, P = .001), and those with asthma (HR 1.70, 95% CI 1.18-2.43, P = .004) were independent risk factors for the development of bipolar disorders in hyperthyroidism patients. Conclusions: Although a possibility that the diagnosis of bipolar disorders in this study actually includes bipolar disorders due to hyperthyroidism cannot be excluded, this study suggests that hyperthyroidism may increase the risk of developing bipolar disorders.